This invention relates to a method and apparatus for adjusting the path of an optical beam. In particular, this invention relates to the adjustment of the path of an optical beam within a fiber-optic communication system.
Optical communication systems typically utilize devices that work with optical signals. For example, optical fibers are used for short and long distance optical transmission. Other devices can also be used in optical communication systems, including filters, multiplexers, modulators, transmitters, receivers, and power splitters to name a few.
Unlike electronic systems that use wire as an electronic conduit, direction and alignment of optical beams and wave guides in optical systems are of increased importance. The core of an optical fiber has a relatively small diameter. Also, optical fibers have relatively narrow acceptance angles within which light is accepted. Accordingly, the light source should be carefully aligned with a receiving fiber in order to avoid coupling losses and other performance problems.
Over the years, various attempts have been made to adjust the paths of optical beams in order to improve their direction and alignment. For example, approaches to steering the beam output (or input) for a pre-made collimator in fiber-optic packaging applications have been proposed. In some applications, steering may be desired when light is to be coupled into or out of the end or tip of a single-mode fiber within a fiber-optic communication system. In such applications, it may be desirable to correct for any slight lateral misplacements of the fiber""s tip.
It is recognized, for example, that laser welding of fibers such as in optical packages can only be controlled to about 1 xcexcm. It is also recognized that adjustment of a beam path in only one dimension is not always sufficient. Moreover, it has been discovered that adjustments often should be finely xe2x80x9ctunedxe2x80x9d or xe2x80x9ctrimmedxe2x80x9d after an initial adjustment is made.
Accordingly, there remains a need for an improved method and apparatus for adjusting the path of an optical beam in such a way as to overcome the deficiencies of the prior art. There also remains a need for a method and apparatus that can steer an optical beam in two dimensions when such adjustment is needed.
This invention provides a lens assembly adapted to adjust the path of an optical beam. The lens assembly includes a support surface positioned adjacent the path of the optical beam, and the support surface defines an aperture through which the optical beam can pass. The support surface is oriented along a plane that traverses the path of the optical beam. A lens of the lens assembly is positioned along the path of the optical beam and extends across the aperture defined by the support surface. The lens is also positioned for movement with respect to the support surface in directions parallel to the plane of the support surface. The lens is configured to adjust the path of the optical beam upon movement of the lens in a direction parallel to the plane of the support surface.
According to another aspect of this invention, a fiber-optic communication system is provided. The communication system includes a fiber-optic cable configured to transmit an optical beam along a path. The fiber-optic cable has an end portion from which the optical beam can be transmitted. A primary lens of the communication system is positioned along the path of the optical beam, and the primary lens is spaced from the end portion of the fiber-optic cable. The primary lens has a focal length selected to converge or diverge the optical beam. A secondary lens of the communication system is also positioned along the path of the optical beam, and the secondary lens is spaced from the primary lens. The secondary lens has a focal length that is larger than that of the primary lens. The secondary lens is positioned for movement along a plane that traverses the path of the optical beam. The secondary lens is configured to adjust the path of the optical beam upon movement of the secondary lens in a direction along the plane.
According to yet another aspect of this invention, a method is provided for adjusting the path of an optical beam transmitted from an end portion of a fiber-optic cable. A primary lens is provided according to the method, with a focal length selected to converge or diverge the optical beam. The primary lens is positioned along the path of the optical beam, and the primary lens is spaced from the end portion of the fiber-optic cable. A secondary lens is provided according to the method, with a focal length that is larger than that of the primary lens. The secondary lens is configured to redirect the optical beam. The secondary lens is positioned along the path of the optical beam, and the secondary lens is spaced from the primary lens. The secondary lens is movable along a plane that traverses the path of the optical beam. The secondary lens is moved in a direction along the plane, thereby adjusting the path of the optical beam.